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Abstract
By isolating phototactic mutants also impaired in thermotaxis we have confirmed that the photosensory and thermosensory transduction pathways converge in Dictyostelium discoideum slugs. Novel features of behaviour of the mutant slugs, normally obscured in ‘wild type’ strains, are the extreme bimodal distribution of directions travelled during phototaxis, and the presence of a second transition from positive to negative thermotaxis at high temperature during migration in thermal gradients. The novel behaviours result from quantitative changes in the transition temperatures during thermotaxis and the preferred angles of deviation (±α) from the direction of the light source during phototaxis. The mutant slugs orient with reduced accuracy in both phototaxis and thermotaxis. These behaviour patterns are consistent with the outcome of mutations impairing signal processing after convergence of photosensory and thermosensory transduction pathways but before adaptation processes operate to set both the preferred directions in bidirectional phototaxis and the transition temperatures in thermotaxis.
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